1. Field of the Invention
The present invention relates generally to projection display devices, and more particularly, to an active matrix type projection display device, typically a rear projection type or a front projection type liquid crystal display device.
2. Description of the Related Art
The development of techniques for manufacturing semiconductor devices, such as a thin-film transistor (TFT), having a semiconductor thin film formed on a low-priced glass substrate, has recently been promoted with the increase in demand for active matrix liquid crystal display devices (liquid crystal panels).
Also, projection type liquid crystal display devices (liquid crystal projectors) have attracted attention, in which pixel portions of liquid crystal panels are irradiated with strong light from a light source, and light passed through the pixel portions is projected to a screen through a lens to form an enlarged image which are enjoyed by a viewer.
FIG. 18 is a diagram schematically showing the construction of a conventional three-panel type liquid crystal projector using three liquid crystal panels. Light source 8001 is a white light source. Each of dichroic mirrors 8002, 8003, 8004, and 8005 reflects only light having wavelengths in a certain wavelength region and allows light having wavelengths in the other regions to pass therethrough. The dichroic mirror 8002 reflects only red light and allows light of the other colors to pass therethrough. The dichroic mirrors 8003 and 8004 reflect only blue light and allow light of the other colors to pass therethrough. Further, the dichroic mirror 8005 reflects only green light and allows light of the other colors to pass therethrough. Mirrors 8006 and 8007 are total reflection mirrors. Liquid crystal panels 8008, 8009, and 8010 are provided to display red, blue and green images, respectively.
FIG. 19 shows the principle of a three-panel type projector. As shown in FIG. 19, a three-panel type projector provides a color image by combining red, green, and blue images.
As shown in FIG. 20, a case where a defective pixel 9001 exists in the liquid crystal panel 8010 (normally white) displaying a green image will be described. If the defective pixel 9001 is a bright dot, it is subjected to processing of irradiation with laser light or the like to be changed into a dark dot.
In the case where a defective pixel 9001 exists in the liquid crystal panel 8010 which displays a green image, a defect due to the dark dot appears in the green image. It is assumed here that each of the liquid crystal panel 8008 displaying the red image and the liquid crystal panel 8009 displaying the blue image has no defective pixel. In the color image formed by combining the three color images, due to the defective pixel in the green image the brightness of the pixel is reduced, and the pixel 9002 with the defect has a purplish color image displayed by combining a red image and a blue image.
Therefore, image in this defective portion is perceptible, thus causes deteriorating the quality of the displayed image.
In view of the above-described problem, an object of the present invention is to provide a display device capable of limiting deterioration of a displayed image even in a case where a display panel having some defective pixels is used.
The present invention is characterized by performing data correction in image display in such a manner that, if there is a defective pixel in a display panel, based on data on positional coordinates determined as the position of the defective pixel, the brightness of other pixels corresponding to predetermined coordinates is increased and the average value of the brightness (referred to as xe2x80x9caverage brightnessxe2x80x9d, hereinafter) of the pixels in a predetermined area is uniform.
As a result of this data correction, the perceptibility of the defect in the image displayed by using the display panel having the defective pixel is reduced, thereby minimizing deterioration of the image.
To determine the positional coordinates of a defective pixel, any of well-known techniques may be used, for example, a method of processing image data obtained by a charge-coupled-device (CCD) camera or the like, a method of checking with only TFTs on the substrate by using an optoelectronic device and a CCD camera, and a method of using a pixel reading circuit mixedly formed on the TFT substrate side.
According to the present invention, a correction table for performing brightness correction is prepared in advance and image data is corrected on the basis of the correction table during ordinary use.
If the defective pixel is not a dark dot but a bright dot, the above-described correction is executed after changing it into a dark dot by repair using laser or the like.
FIG. 1 shows a case of combining red, green and blue images into a color image in a three-panel type projection display device.
In the example shown in FIG. 1, a defective pixel 101 exists in a display panel displaying the green image. It is assumed here that the defective pixel 101 is a dark dot. If the defective pixel 101 is a bright dot, it is changed into a dark dot by a process using laser or the like. Consequently, a defect formed by the dark dot appears in the green image. It is also assumed that each of the display panel displaying the red image and the display panel displaying the blue image has no defective pixel and displays a normal image. Conventionally, in the combination of red, green and blue images, the green image in the color image has a zero level of brightness at a certain position represented by coordinates, due to the existence of a pixel defect in the green image, only the red and blue images are combined to display a purplish image on a pixel 104 which has the defect. The pixel 104 is easily perceptible in the resulting image, and cannot obtain good display quality.
According to the present invention, as shown in FIG. 1, brightness correction is performed with respect to the pixels in the display panel displaying the red image and the display panel displaying the blue image which have the same coordinates (m, n) as the defective pixel in the display panel displaying the green image (more specifically, correction of increasing the average brightness of the pixels 102 and 103). The human sense of sight is higher in lightness sensitivity than in chromaticity sensitivity. Therefore, by only increasing the brightness of the pixels having the same coordinates as the defective pixel, the defective pixel in the resulting image obtained by combining the images of the three display panels becomes harder to percept. In this manner, deterioration of the image can be minimized as much as possible.
The concept of the present invention has been described with an example of a case where a defective pixel exists in a green display panel in a projection display device using three display panels. Needless to say, the present invention is also effective in a case where a defective pixel exists in the red or blue display panels.
The configuration of this invention is described below.
The configuration of the invention disclosed in this application is:
a defective pixel compensation system wherein in a projection display device having three display panels, the system comprises:
means for specifying one of the display panels having a defective pixel out of the three display panels;
means for specifying coordinates of the defective pixel; and
means for increasing the brightness of pixels having the same coordinates as the coordinates of the defective pixel in the display panels other than the one display panel having the defective pixel out of the three display panels.
Further, as shown in FIG. 3, the other aspect of the present invention disclosed in this application is characterized in that compensation is carried out to increase brightness of pixels adjacent to the defect pixel of the green display panel in addition to the above structure. While increasing the brightness of the pixel having the same coordinates as the defect pixel, compensation is conducted for increasing the brightness of the adjacent pixels. As the result, the defect pixel in the combined image of images of the three display panels are not remarkable and it is possible to prevent as much as possible the deterioration of the image.
Here, an example of a green display panel, in which defect pixels exist, is shown in a projection display device using three display panels, but needless to say, it is not particularly limited to green display panels.
A defective pixel compensation system for use in a projection display device having three display panels, said system comprising:
means for specifying one of the three display panels having a defective pixel;
means for specifying coordinates of the defective pixel;
means for increasing the brightness of at least one of pixels having coordinates adjacent to the coordinates of the defective pixel; and
means for increasing the brightness pixels having the same coordinates as the defective pixel in the display panels other than the display panel having the defective pixel out of the three display panels.
A projection display device comprising:
a light source;
an optical system for separating light emitted from said light source into three fluxes of light;
a group of three display panels including one display panel having at least one defective pixel;
an optical system for combining images formed by said three display panels while projecting the images onto a screen; and
a defective pixel compensation system for increasing the brightness of pixels having the same coordinates as the defective pixel in the display panels other than the display panel in which the defective pixel exists.
A defective pixel compensation system for use in a display device having one display panel with a defective pixel, the system comprising:
means for determining positional coordinates of the defective pixel; and
means for increasing the brightness of pixels having coordinates adjacent to the coordinates of the defective pixel.
That is, in a direct-view type display device using one display panel, data correction is performed by increasing the brightness of pixels adjacent to the defective pixel in the display panel. This correction, based on increasing the brightness of the adjacent pixels, reduces the perceptibility of the defective pixel in the image of the display panel, thereby minimizing deterioration of the image. This correction is particularly effective in a case where the pixel size is extremely small.